In a frame transfer CCD image sensor, an image pickup portion is constituted by arranging a plurality of CCD shift registers each provided with an opening to incident light on a channel region, each bit of the CCD shift registers independently constituting a light-sensitive pixel. That is, at exposure, a clock voltage applied to a transfer electrode group disposed corresponding to each of the bits is controlled to form a potential well for each bit, and thereby a signal charge generated in accordance with light incident on the bit is accumulated in the bit. On the other hand, when an exposure period is over, the signal charge accumulated in each of the bits is transferred to an storage portion by driving the CCD shift register, followed by sequentially reading from the storage portion.
The light-sensitive pixels arranged in a column direction on the CCD shift register of the image pickup portion are formed on consecutive channel regions. Accordingly, the light-sensitive pixels adjacent to each other are fundamentally brought into contact. Color filters and interlayer films are laminated on a semiconductor substrate region constituting light-sensitive pixels. Since the light-sensitive pixels are in contact with each other in a column direction, when light enters obliquely at a boundary region of pixels, light transmitted through the color filter does not enter a light-sensitive pixel assigned to the color filter, but instead enters a light-sensitive pixel assigned to an adjacent color filter of a different color, and as a result color mixing is likely to occur. Furthermore, light incident on the boundary portion of pixels, owing to the refraction by the interlayer film, may cause crosstalk between the pixels.
As a countermeasure against this problem, it is proposed to dispose a light shield at the boundary portion of pixels. FIG. 1 is a plan view showing a structure of a so far proposed-image pickup portion. On a region corresponding to the image pickup portion on a surface of a semiconductor substrate, a plurality of CCD shift register channels 2 extending in a colum direction is formed mutually separated from each other by a channel stop (device isolation region) 4 from each other. On the semiconductor substrate, a plurality of transfer electrodes 6 that are orthogonal to the channels 2 and arranged in a column direction are laminated and formed. The transfer electrode 6 is formed of a light-transmissive material such as polysilicon. On the transfer electrode 6, a layer of metal such as aluminum (Al) having the light-shielding property is laminated and patterned, and thereby a clock wiring 8 extending on the channel stop 4 is formed. The clock wiring 8 is electrically connected through a contact 10 to the transfer electrode 6, and thereby a transfer clock can be applied to the transfer electrode 6.
In the CCD shift register constituting the image pickup portion, a three-phase drive with transfer clocks φ1 through φ3 is used, and three transfer electrodes 6-1 through 6-3 lying consecutively in the column direction constitute 1 bit of the shift register. The bit is assigned to the light-sensitive pixel of the image pickup portion. For instance, when a portion from the transfer electrode 6-1 to which a transfer clock φ1 is applied, extending to the transfer clock 6-3 to which a transfer clock φ3 is applied, is assumed to constitute 1 bit, there is a boundary of light-sensitive pixels between the transfer electrode 6-1 and the transfer electrode 6-3. A color filter is disposed on each of the light-sensitive pixels. For instance, here, the color filters are arranged in a Bayer matrix and color filters that are different in color 12-1 and 12-2 are interleaved in each column.
A light shield 14 disposed at the boundary portion between pixels, when the light shielding metal layer is patterned, is formed simultaneously with the clock wiring 8.
The light shield 14 is formed as a pattern located on the channel 2 and separated from both clock wirings 8 on both sides of the channel. That is, a gap of the light-shielding metal layer is disposed on each of portions between the light shield 14 and the clock wirings 8 on both sides. Light obliquely incident on the gap portion causes crosstalk and color mixing between adjacent pixels in the column direction. Accordingly, the light shield 14 cannot sufficiently inhibit color mixing or the like from occurring.